Confined field magnet system and method

Abstract

A system and method of generating a magnetic field that is uniform in magnitude and direction may generally restrict the field from expanding away from a longitudinal axis. In some instances, such a magnetic field may be controllable in magnitude and direction. In accordance with some embodiments, a generated magnetic field may be selectively confined to a predetermined three-dimensional space.

1. A method of producing a magnetic field having a controllable magnitude and direction within a field space; said method comprising:
 defining two orthogonal field components wherein a first field component is to be generated along a first longitudinal axis and a second field component is to be generated along a second longitudinal axis; 
 positioning a plurality of pole faces at locations along each of the first and second longitudinal axes; and 
 for each of the two orthogonal field components:
 selecting a first magnetostatic potential to apply to a first plurality of longitudinal pole faces at a first longitudinal boundary oriented substantially normal to a longitudinal axis; 
 selecting a second magnetostatic potential to apply to a second plurality of longitudinal pole faces at a second longitudinal boundary oriented substantially normal to the longitudinal axis; 
 identifying a plurality of lateral pole faces disposed along a lateral boundary intermediate the first and second longitudinal boundaries; each respective one of the plurality of lateral pole faces disposed in a respective lateral boundary plane oriented substantially normal to the longitudinal axis; and 
 for each respective one of the plurality of lateral pole faces, selecting a value of a respective magnetostatic potential in accordance with a position of the respective lateral boundary plane relative to the first and second longitudinal boundaries; 
 
 
       and
 supplying selected values of magnetostatic potential to each of the plurality of pole faces; 
 thereby creating a substantially uniform magnetic field that is controllable in magnitude and direction within the field space. 
 
     
     
       2. The method of  claim 1  wherein, for each of the two orthogonal field components, said supplying comprises connecting each of the plurality of pole faces through a magnetic conduit to a magnetostatic potential generator to provide the selected values of magnetostatic potential. 
     
     
       3. The method of  claim 1  wherein, for each of the two orthogonal field components, the first magnetostatic potential has a value of P(L a ), the second magnetostatic potential has a value of P(L b ), and the respective magnetostatic potential, P(T i ), supplied to a respective one of the plurality of lateral pole faces has a value that is substantially equal to 
       
         
           
             
               
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       where sa i  is a distance between a respective lateral boundary plane, i, and the first longitudinal boundary and sb i  is a distance between the respective lateral boundary plane, i, and the second longitudinal boundary, and s is a distance between the first and second longitudinal boundaries. 
     
     
       4. The method of  claim 2  wherein, for each of the two orthogonal field components, said supplying further comprises:
 identifying adjacent ones of the plurality of lateral pole faces connected to the magnetic conduit; 
 coupling a magnetomotive force generator to the magnetic conduit between the respective lateral boundary planes of the adjacent pole faces; and 
 generating a magnetomotive force having a value substantially equal to a difference in the respective magnetostatic potentials selected for the adjacent pole faces responsive to said selecting. 
 
     
     
       5. The method of  claim 4  wherein, for each of the two orthogonal field components, said generating comprises driving an electric current through a current carrying conductor coiled around the magnetic conduit, and wherein the magnetomotive force is a product of a number of turns in the coil and an amplitude of the electric current. 
     
     
       6. The method of  claim 5  wherein the value of the magnetomotive force is selectively adjustable in accordance with said driving. 
     
     
       7. The method of  claim 4  wherein the value of the magnetomotive force is proportional to a distance between the respective lateral boundary planes of the adjacent pole faces. 
     
     
       8. The method of  claim 1  wherein said selecting the first, second, and respective magnetostatic potentials comprises deriving, for each respective one of the plurality of pole faces, a first component magnetostatic potential value associated with the first orthogonal field component and a second component magnetostatic potential value associated with the second orthogonal field component. 
     
     
       9. The method of  claim 8  wherein said supplying comprises providing each respective one of the plurality of pole faces a magnetostatic potential having a magnitude equal to the sum of the first and second component magnetostatic potential values, thereby controlling the magnitude and direction of the magnetic field. 
     
     
       10. The method of  claim 1  wherein each of said plurality of pole faces has a dimensional profile and wherein the method further comprises:
 aligning the plurality of pole faces along the first longitudinal axis and the second longitudinal axis such that the dimensional profiles define two pairs of boundary surfaces to confine the field space. 
 
     
     
       11. The method of  claim 10  wherein a first pair of boundary surfaces is oriented substantially parallel to the first longitudinal axis and wherein a first surface of the first pair is disposed on an opposite side of the first longitudinal axis from a second surface of the first pair. 
     
     
       12. The method of  claim 11  wherein a second pair of boundary surfaces is oriented substantially parallel to the second longitudinal axis and wherein a first surface of the second pair is disposed on an opposite side of the second longitudinal axis from a second surface of the second pair. 
     
     
       13. The method of  claim 12  wherein the two pairs of boundary surfaces and a spatial extent of the dimensional profiles normal to the first and second longitudinal axes define a three dimensional space, and wherein the method further comprises generating the magnetic field to have a substantially uniform magnitude and direction at a utilization region within the three dimensional space. 
     
     
       14. The method of  claim 13  further comprising shaping the dimensional profiles to optimize uniformity of the magnetic field at the utilization region. 
     
     
       15. The method of  claim 13  further comprising shaping the dimensional profiles and the pairs of boundary surfaces to define the dimensional space in accordance with physical dimensions of an object under test. 
     
     
       16. The method of  claim 15  further comprising positioning the object under test within the utilization region, exposing a magnetic component of the object under test to the magnetic field, and controlling the magnitude and direction of the magnetic field by adjusting values for the two orthogonal field components. 
     
     
       17. The method of  claim 16  wherein said exposing comprises sequentially exposing the magnetic component of the object under test to different magnetic fields. 
     
     
       18. The method of  claim 17  wherein the different magnetic fields have different magnitudes. 
     
     
       19. The method of  claim 17  wherein the different magnetic fields have different directions. 
     
     
       20. An apparatus for producing a substantially uniform magnetic field having a controllable magnitude and direction within an area defined by boundaries; said apparatus comprising, for each of the boundaries:
 a respective plurality of pole pieces associated with a respective boundary, each of said plurality of pole pieces having a pole face with a dimensional profile; said dimensional profiles of said pole faces defining a boundary surface for the respective boundary; and 
 a respective plurality of magnetomotive force generators associated with the respective boundary, each of said plurality of magnetomotive force generators disposed between respective adjacent pole pieces along the respective boundary and coupled to provide selected values of magnetomotive force to respective pole faces of said adjacent pole pieces in accordance with positions of said respective pole faces along the respective boundary, thereby creating the substantially uniform magnetic field that is controllable in magnitude and direction within the area. 
 
     
     
       21. The apparatus of  claim 20  wherein each of said plurality of magnetomotive force generators produces a magnetomotive force having a value that is proportional to a distance between said respective pole faces. 
     
     
       22. The apparatus of  claim 20  wherein each of said plurality of magnetomotive force generators comprises a coil winding of current carrying conductor coiled around a magnetic conduit, and wherein the magnetomotive force is a product of a number of turns in said coil winding and an amplitude of an electric current driven through said current carrying conductor. 
     
     
       23. The apparatus of  claim 22  wherein said magnetic conduit comprises a soft magnetic material and wherein said magnetic conduit is dimensioned in accordance with a magnetic permeability value and a magnetic saturation value associated with said soft magnetic material. 
     
     
       24. The apparatus of  claim 22  wherein said magnetic conduit comprises a magnetic yoke having a respective extension connecting said magnetic yoke to a respective pole piece. 
     
     
       25. The apparatus of  claim 24  wherein each of said plurality of magnetomotive force generators comprises a coil winding of current carrying conductor coiled around said magnetic yoke between adjacent extensions. 
     
     
       26. The apparatus of  claim 25  wherein said coil windings are electrically connected in series and energized with an activation current. 
     
     
       27. The apparatus of  claim 26  wherein a distance between each pair of adjacent pole faces is substantially uniform and wherein each of said coil windings has the same number of turns. 
     
     
       28. The apparatus of  claim 20  wherein said pole pieces comprise a soft magnetic material; each of said pole pieces having a respective magnetic permeability value and a respective magnetic saturation value associated with said soft magnetic material. 
     
     
       29. The apparatus of  claim 28  wherein each of said pole pieces is dimensioned in accordance with the respective values. 
     
     
       30. The apparatus of  claim 29  further comprising a drive circuit to control said plurality of magnetomotive force generators as a function of a magnitude of the magnetic field to be produced. 
     
     
       31. The apparatus of  claim 20  further comprising a central axis within the area defined by boundaries and located substantially equidistant from each of the boundaries, and wherein said dimensional profile of each said pole face is located in a plane extending radially from the central axis. 
     
     
       32. The apparatus of  claim 31  wherein said dimensional profile of each said pole face is scaled in accordance with azimuth. 
     
     
       33. The apparatus of  claim 31  wherein said dimensional profiles of said pole faces are shaped and oriented such that positions of said dimensional profiles along the respective boundary change congruently as a function of elevation along the central axis. 
     
     
       34. An apparatus for producing a substantially uniform magnetic field within defined substantially rectilinear boundaries, wherein said field has a controllable magnitude and a controllable azimuthal direction relative to a central axis that is substantially equidistant from each of the substantially rectilinear boundaries; said apparatus comprising, for each of the substantially rectilinear boundaries:
 a respective plurality of pole pieces associated with a respective boundary, each of said plurality of pole pieces having a pole face with a dimensional profile; said dimensional profiles of said pole faces defining a boundary surface for the respective boundary; and 
 a respective plurality of magnetomotive force generators associated with the respective boundary, each of said plurality of magnetomotive force generators disposed between respective adjacent pole pieces along the respective boundary and coupled to provide selected values of magnetomotive force to respective pole faces of said adjacent pole pieces in accordance with positions of said respective pole faces along the respective boundary. 
 
     
     
       35. The apparatus of  claim 34  wherein said dimensional profile of each said pole face is located in a plane oriented normal to the respective boundary. 
     
     
       36. The apparatus of  claim 34  wherein said dimensional profile of each said pole face is located in a plane extending radially from the central axis. 
     
     
       37. The apparatus of  claim 36  wherein said dimensional profile of each said pole face is scaled in accordance with azimuth. 
     
     
       38. The apparatus of  claim 36  wherein said dimensional profiles of said pole faces are shaped and oriented such that positions of said dimensional profiles along the respective boundary change congruently as a function of elevation along the central axis. 
     
     
       39. A method of producing a magnetic field having a controllable magnitude and direction within a field space; said method comprising:
 defining a field plane having two orthogonal axes, each of the axes being a longitudinal axis for one of two orthogonal field components, wherein a first field component is to be generated along a first longitudinal axis and a second field component is to be generated along a second longitudinal axis; 
 defining a spatial boundary in the field plane, the spatial boundary comprising a respective pair of boundary surfaces aligned parallel to each respective longitudinal axis; 
 positioning a plurality of pole faces at the boundary surfaces; 
 for a respective field component, designating ones of the plurality of pole faces at the boundary surfaces perpendicular to the respective longitudinal axis as longitudinal pole faces and designating ones of the plurality of pole faces at the boundary surfaces parallel to the respective longitudinal axis as lateral pole faces; 
 selecting a magnitude of each of the first and second field components; 
 for each of the first and second field components:
 producing the field component by: selecting a first magnetostatic potential to apply to the longitudinal pole faces at a first longitudinal boundary surface; and selecting a second magnetostatic potential to apply to the longitudinal pole faces at a second longitudinal boundary surface; 
 and 
 confining the field component by, for each of the lateral pole faces: selecting a value of a respective magnetostatic potential intermediate the first and second magnetostatic potentials; the respective magnetostatic potential being selected in accordance with a position of the lateral pole face relative to the first and second longitudinal boundary surfaces; 
 wherein said selecting values of the first, second, and respective magnetostatic potentials comprises selecting magnetostatic potentials that are proportional to the selected magnitudes of each of the first and second field components; 
 
 and 
 
       for each of the plurality of pole faces, supplying a value of magnetostatic potential that represents a sum of the values selected in accordance with said producing and said confining with respect to the first and second field components; thereby creating a substantially uniform magnetic field that is controllable in magnitude and direction within the field space.